Transformer protective device



April 7, 1954 D. R. GODFREY 2,677,113

TRANSFORMER PROTECTIVE DEVICE Filed Jan. 30, 1955 WITNESSES:

Patented Apr. 27, 1954 TRANSFORMER PROTECTIVE DEVICE Donald R. Godfrey, Sharon, Pa., assignor to Westinghouse Electric Cor Pa., a corporation of This invention relates to transformers and more particularly to protective means associated therewith.

The output voltage of transformers is oftentimes varied by means of a tap-changer associated therewith. When a tap-changer i used, it must be capable of effecting a change in the output Voltage of the transformer without interrupting the input or output circuits of the transformer. In order to accomplish this operation under load, it is necessary to provide at least two moving contact members so that one of the moving contact members will at all times maintain an uninterrupted electrical circuit from the input to the output of the transformer. However, when the movable contact members are in engagement with different stationary contact members, the current flow through these movable contact members would be excessive unless a preventive autotransformer were connected thereto.

When the tap-changer is rotated beyond its minimum or maximum position, the preventive autotransformer is connected across all the tapped portion of the transformer windings, thus causing excessive current to flow through the preventive autotransformer. In most transformers having a tap-changer associated therewith, a stop mechanism is provided to prevent the rotation of the tap-changer beyond these minimum and maximum positions. However, in such stop mechanisms which do not reset themselves automatically, means must be provided to reset the stop mechanism manually. When the stop mechanism is reset manually, it is then possible to continue to change the position of the tap-changer and connect the preventive autotransformer across all of the tapped portion of the transformer winding and thereby damage the transformer.

An object of this invention is to provide for preventing damage to a preventive autotransformer incorporated in a transformer tapchanger, by so coordinating a stop mechanism with the tap-changer that it i impossible to actuate the tap-changer beyond its normal operating range in either a minimum or maximum direction.

A further object of this invention is to provide for automatically resetting a tap-changer stop mechanism once the tap-changer has been actuated to either of its extreme positions and then actuated a predetermined distance in the direction of its normal operating range, by so positioning one of two coordinated cam members by means of a stop bar tripped in response to the extreme positioning of the tap-changer, that the poration, East Pittsburgh,

Pennsylvania Application January 30, 1953, Serial No. 334,313

7 Claims. (Cl. 336-) stop bar rides the surface of the positioned cam member while the tap-changer is being actuated in its normal operating range to thereby effect a resetting of the stop bar.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which:

Figure 1 is a schematic diagram of apparatus and circuits illustrating an embodiment of the teachings of this invention;

Fig. 2 is a view in elevation of a portion of the sto mechanism illustrated in Fig. 1, which portion is shown in the unactuated position;

Fig. 3 is a view in section of the portion of the stop mechanism illustrated in Fig. 2, the sectional view being taken along the line III-III;

Fig. 4 is a view in elevation of a portion of the stop mechanism illustrated in Fig. 1, which portion is shown in the actuated position; and

Fig. 5 is a schematic diagram showing the position of the transformer tap-changer when the stop mechanism is in the position as illustrated in Fig. 4.

Referring to Fig. 1, there is illustrated an autotransformer In having a fixed winding l2 and a tapped winding l 4, which receive energy from the supply terminals 15 and I5 and supply energy to the load terminals l 6 and It. In order to vary the amount of the tapped winding [4 that is connected in circuit relationship with the fixed winding I2, a tap-changer l! is electrically connected to the tap winding l4 and to the fixed winding I2 of the transformer l0. However, in order to prevent the tap-changer I! from being actuated beyond the minimum and maximum limits of its operating range to thereby cause damage of the tap-changer I], a stop mechanism l8 responsive to the positioning of the tap-changer I1 is provided.

Referring more particularly to the tap-changer l1, it is to be noted that the tap-changer I! includes two movable contact members 22 and 24 which are actuated by either a reversible motor 26 or by a hand crank 28 through suitable mechanical linkages which will be described in greater detail hereinafter. As can be seen from the drawing, one end of the movable contact member 2?. remains in electrical contact with a conducting ring 30 when the contact member 22 is being actuated into its various positions around the ring 30 by means of either the motor 26 or the hand crank 28. As the movable contact member 22 is being actuated through its various positions, the other end of the contact member 22 engages a plurality of stationary contact members 34, as, 38, ill, 42, M, 56, it and so, which are electrically connected to the tapped winding 54 of the transformer iii. In like manner, one end of the movable contact member engages these stationary contact members 3 36, 31-3, 4%, 42, ts, 46, 48 and 58, as it is actuated through its various positions. However, the other end of the movable contact member 24 during these various positions remains continually in electrical contact with a conduct ing ring 52.

In order to connect the tapped winding l4 so that its turns either aid or buck the turns of the fixed winding l2, a reversing switch c is provided. In this instance, the reversing switch. comprises two stationary contact members and 5% which are selectively engaged by a movable contact member so. As illustrated, the stationary contact 56 is electrically connected to one end of the tapped winding Ill, and the stationary contact member 58 is electrically connected to the other end of the tapped winding i i.

For the purpose of interconnecting the fixed winding l2 with the tapped winding it, one end of the fixed winding i2 is electrically connected to the movable contact member iii} of the selector switch 54. As can be seen from the drawing, the load terminal I3 is also electricall3, connected to the movable contact member 88 as well as to the stationary contact member 56 of the tap-changer ll.

As illustrated, a preventive autotransformer 62 is electrically connected to the conducting rings Bil and 52, through conductors 66 and 68, respectively, in order to prevent an excessive flow of current through the conductors t5 and 63 when these conductors are electrically connected by means of the tap-changer ll across a portion of the tapped winding Hi. The sequence of operation of the movable contact members 22 and 24 of the tap-changer IT, as they move through their various tap-changing positions, will be described hereinafter.

In accordance with the teachings of this invention, the stop mechanism is is provided in order to ensure that the tap-changer ii cannot be actuated beyond its extreme positions of min imum and maximum output for the autotransformer iii, which action would cause damage to the preventive autotransformer since it would then become connected across all of the tapped winding i l. The stop mechanism i3 is also pro vided so that there is no need to reset the mechanism by hand, which, hereinbefore mentioned, gives rise to the danger of damaging the preventive autotransformcr 62. The stop mechanism iii automatically resets itself, as will be explained more fully hereinafter.

As illustrated, the stop mechanism is comprises a spring-loaded stop bar i=3 which has a notch 72 disposed inside thereof. One end 14 of a trip latch is is disposed in the notch 12 of the stop bar H3 in order to maintain it in the spring loaded position during the normal tapchanging operation of the tap-changer H. In this instance, the lower end of the trip latch 75 is actuated by a trip bar 18 in order to disengage the end M of the trip latch Iii from the notch '12 of the stop bar H3 to thereby permit the compression spring 80 to actuate the stop bar iii into engagement with the component parts of a stop disk 82 and thereby prevent the further actuation of the tap-changer I! in a given direc tion.

In practice, the stop disk 82, and either the movable contact member 22 or the movable contact member 24 of the tap-changer II, are actuated simultaneously by either the hand crank 28, manual operation is desired, or by the motor 26 ii motor operation is desired. In this instance, the hand crank 28 and the motor 29 are mechanically connected to the stop disk 82 through a pair of bevel gears 90, the stop disk 82 in turn being mechanically connected to the movable contact members 22 and 24 of the tap changer I7 through a pair of bevel gears 92 and suitable gearing 94.

The hand crank 23 and motor 26 are alslo mechanically connected to the trip bar iii through suitable gearing 96 and a pair of bevel gears 33, the gearing 94 and 9t being such that when the tap-changer I! is actuated into one extreme position, such as to give a minimum output voltage from the transformer ID, the trip bar l8 will be in position to actuate the trip latch 16, and the component parts of the stop disk 82 will be in proper position to receive the stop bar Hi. The gearing 94 and 95 must also be such that when the motor 26 or hand crank 28 actuates the tap-changer II to the other ex treme position, such as to give a maximum output voltage from the transformer ill, the trip bar it? will be again in position to actuate the trip latch 16, and the stop disk 82 will be in proper position to receive the stop bar iii. In practice, a tension spring Hill is connected to the trip latch '16 in order to force the end i l of the trip latch 15 into engagement with the notch '52 once the trip bar 10 has been actuated to the position shown in Fig. 1.

If the motor 26 is used to actuate the movable contact members 22 and 24 of the tap-changer ll, some means must be provided in order to stop the motor 26 once these movable contact members reach their extreme positions in either a maximum or minimum direction. In order to deenergize the motor 26 once either of these ex treme positions is reached, a collar I82 is suitably connected to the stop bar it. In this in stance, the collar W2 is mechanically connected to a movable contact member Hill which is disposed to make electrical contact with stationary contact members H16, H38. When the stop bar it is tripped, the movable contact member li is actuated to the circuit interrupting position, thereby interrupting the supply of energy to the motor 26 which is received from supply terminals ")5 and Hill.

Referring to Figs. 2 and 3 of the drawing, the stop disk 62 and its associated component parts are shown in greater detail. As illustrated, two L-shaped cam members lid and iii pivoted about two predetermined points H2 and lid, respectively, on the stop disk 82. A. plate member H6 is suitably secured to the stop disk 82 and is disposed above the cam members iii and iii in order to prevent the cam members lie and Hi from lifting vertically under load. In this instance, the cam members i It and i i have disposed therein spring-loaded pin members lit and I22, respectively, which pin members are held in the spring-loaded position by the plate member IIB when the cam members are posi' tioned, as shown in Fig. 2.

In order to bias the cam members lit and ill in a direction towards one another, a spring member I24 is mechanically connected to each of the cam members H0 and HI. Associated with the cam members H0 and iii are protruding stop members I30 and I32 which prevent the cam '5 I members i H] and I I l,'respectively, from being rotated beyond a predetermined position, and thereby prevent the further rotation of the stop disk 32. In this instance, the stop members iii; and S32 are an integral part of the stop disk 82.

The operation of the apparatus shown in Fig. 1 can be more clearly understood by referring to Figs. 4 and 5 in conjunction with Fig. 1. For instance, the output voltage of the transformer Ill, as it appears across the load terminals I5 and IE, is at a minimum when the movable contact members 22 and 24 of the tap changer i! are both in electrical contact with the stationary contact member 48, and the movable contact member 60 in electrical contact with the stationary contact member 53. In order to increase the output voltage of the transformer Iii, the hand crank 28 is rotated in a clockwise direction to thereby actuate the movable contact member 22 to such a position that it engages the stationary contact 46. The output voltage of the transformer I is further increased by rotating the hand crank 28 further in the clockwise direction to thereby actuate the movable contact member E i so that it too makes electrical contact with the stationary contact member 68. This sequence of positioning of the movable contact members and 24 is continued by rotating the crank 2a in a clockwise direction until both the movable contact members 22 and 24 are in electrical contact with the stationary contact member 3 of the tap-changer IT. Up to this position, the turns of the tapped winding i it aid the turns of the fixed winding I2. Then the hand crank 28 is rotated further in the clockwise direction until the movable contact member 22 makes electrical contact with the stationary contact member 50. The hand crank 23 is then further ro tated in a clockwise direction to actuate the movable contact member 24 so that it will make elec trical contact with the stationary contact member 50, and as soon as the movable contact member 24 breaks contact with the stationary contact member 34, the movable contact member 66 of the reversible switch 5:3 is actuated so as to make electrical contact with the stationary contact member 56.

With both the movable contact members 22.

and 24 in electrical contact with the stationary contact member 5a and the movable contact member Ell of the reversing switch 54 in electrical contact with the stationary contact member 56, the tap-changer is in the neutral position in which the input and output voltages are substantially equal. By rotating the hand crank further in the clockwise direction, the output voltage of the transformer It is further increased since the turns of the tapped winding M are new bucking the turns of the fixed winding The output voltage of the transformer it continues to increase as long as the hand crank 28 is further rotated in a clockwise direction and the stop disk 82 is thereby further rotated a counterclockwise direction until finally both the movable contact members 22 and 2d of the tap-changer I! engage the stationary contact member 34. Once this position is reached, the trip bar 18 actuates the trip latch E6 to thereby disengage the end 14 from the notch '52 in the trip bar It and thereby permit the trip bar 7!! to move to the right under the force of the spring it'd until it engages the cam member il On further rotation of the stop disk iii in the counterclockwise direction, the trip bar it efof the reversing switch 54 is fects a rotation of the cam member He about its pivot point H2 until the leg I46 of the cam member H0 rests against the protruding stop member I 30, thus preventing any further rotation of the stop disk 82 in the counterclockwise direction. When this position of the stop disk 82 is reached, as shown in Fig. 4, the movable con tact members 22 and 24 are positioned as shown in. Fig. 5. Therefore, when the movable contact member 58 of the reversing switch 513 is in electrical contact with the stationary contact mem ber 56, is it impossible to actuate the movable contact member 22 of the tap-changer l1 until it engages the stationary contact member 55! to thereby electrically connect the preventive autotransformer across the tapped portion of the tapped winding 54, which would cause injury to the preventive autotransformer.

When the cam member i H! is rotated about its pivot point H2, the spring-loaded pin member i2!) is permitted to extend beyond the plate member H 6, and when in this spring unloaded position, it rests against the edge of the plate member i it under the influence oi the spring member 22d, and thus the cam member IN] is prevented from returning to its original position. On rotating the hand crank 28 in a counterclockwise direction to return the tap-changer to its normal operating range, the stop bar 16 slides along the surface of the cam member Hi3 until it is reset. This resetting occurs when the stop bar l0 has moved far enough to the left to per mit the end "M of the trip latch is to again enter the notch E2 of the stop bar under the force of the spring Hill.

Once the hand crank 28 has been turned further in a counterclockwise direction to thereby rotate the stop disk 22 a predetermined distance in the opposite direction, the pin member I25! disposed in the cam member 1 I6 is reset by means of a reset mechanism I42 shown in Fig. 3. In order to return the output voltage of the transformer It to its minimum value, the hand crank 28 is rotated further in a counterclockwise direction until both the movable contact members 22 and 2d are in electrical contact with the stationar contact member 48 of the tap-changer i1, and the movable contact member 66 of the reversing switch 54 is in electrical contact with the stationary contact member 58. Further actuation of the movable contact member it so that it would engage the stationary contact member 5!] of the tap changer ll is prevented by the stop mechanism 58. If the movable contact member 23 were permitted to make electrical contact with the stationary contact member 5b, the preventive autotransformer 62 would be electrically connected across the tapped portion of the tapped winding it, thus causing injury thereto. Such action is prevented since before the movable contact member 24 reaches the stationary contact mem ber 50 of the tap changer 7!], the stop bar iii is tripped to thereby engage the cam member HI and thus rotate it about its pivot point He into engagement with the protruding stop member I32. Such an action permits the spring-loaded pin member 122 of the cam member Hi to extend beyond the plate member H6 and thereby engage the edge of the plate member. The spring member I2 1 then biases the pin member 522 against the edge of the plate member i 15, holding the cam member H i in such a rotated position that the trip bar Hi slides along the surface of the cam member Hi when the hand crank 28 is rotated in a clockwise direction. By sliding along the surface of the cam member :ill in this manner, the stop bar 10 is reset and assumes the position illustrated in Fig. 1. On further rotation of the hand crank 28 in a clockwise direction, the pin member $22 is reset by the reset mechanism I42 to thereby permit the spring member I24 to rotate the cam member l l 3 about its pivot point H l until it assumes the position illustrated in Fig. 2.

From the above discussion, it is realized that the tap-changer I! cannot be actuated beyond the maximum and minimum limits of its oper ating range since the stop mechanism ill prevents such further rotation. In addition, the stop mechanism [8 automatically resets itself. Thus, no manual resetting of the apparatus is necessary, which heretofore gave rise to injuries to the apparatus as hereinbefore mentioned.

Since certain changes may be made in. the above apparatus and circuits, and dirIeren-t embodiments of the invention may he made without departing from the scope thereof, it is intended that all matter contained. in the above description or shown in the accompanying drawing sh .7. be interpreted as illustrative and not in a. limiting sense,

I claim as my invention:

1. In a transformer whose output voltage is varied by means of a tap-changer associates therewith, the combination comprising, a stop mechanism including a stop bar, a stop disk disposed to cooperate with the stop bar, two members pivoted about two predetermined points on the stop disk, means for simultaneously rotating the stop disk and for positioning the tapchanger, means for tripping the stop bar once the tap-changer has reached a predetermined position to thereby effect engagement of the stop bar with one of the cam members and thus prevent further positioning of the tap-changer and rotation of the stop disk in a given direction, the engaging of said one of the cam members by the stop bar effecting a rotation of said one of the members about its pivot point to thereby assume a new position, and means for preventing said one of the cam members from returning to its original position until the stop disk rotates a predetermined distance in the opposite direction, whereby the stop bar slides along the surface or said one of the cam members as the stop disk rotates in said opposite direction to thereby effect a resetting of the stop bar.

2. In a transformer whose output voltage is varied by means of a tap-changer associated therewith, the combination comprising, a stop mechanism including a stop bar, a stop disk disposed to cooperate with the stop bar, two cam members pivoted about two predetermined points on the stop disk, a spring member connected to each of the cam members for biasing the cam members in a direction towards one another, means for simultaneously rotating the stop disk and for positioning the tap-changer, means for tripping the stop bar once the tap-changer has reached a predetermined position to thereby eirect engagement of the stop bar with one of the cam members and thus prevent further position" ing of the tap-changer and rotation of the stop disk in a given direction, the engaging of said one of the cam members by the stop bar effecting a rotation of said one of the cam members about its pivot point to thereby extend the spring member, and means for preventing said one of the cam members from returning to its original position by the action of the spring member until the stop disk rotates a predetermined distance in the opposite direction, whereby the stop bar slides along the surface of said one of the cam members as the stop disk rotates in said opposite direction to thereby effect a resetting of the stop bar.

3. In a transformer whose output voltage is varied by means of a tap-changer associated therewith, the combination comprising, a stop mechanism including a stop bar, a stop disk disposed to cooperate with the stop bar, means for simultaneously rotating the stop disk and positioning the tap-changer, two cam members pivoted about two predetermined points on the stop disk, each cam member having disposed therein a spring-loaded pin member, a plate member disposed to cooperate with the pin members and hold them in the spring-loaded position during the normal positioning of the tap-changer, a spring connected to each of the cam members for biasing the cam members in such a direction as to enable the plate member to hold the pin members in the spring-loaded position during the normal positioning of the tap-changer, means for tripping the stop bar once the tap-changer has reached a predetermined position, to thereby effect an engagement of the stop bar with one of the cam members, rotating it about its pivot point, extending the spring member and permitting its spring-loaded pin member to extend beyond the plate member and thereby preventing further rotation of the stop disk and positioning of the tap-changer in a given direction, and means for resetting the spring-loaded pin member of said rotated cam member once the stop disk has been rotated a predetermined distance in the opposite direction, the stop bar during a portion of this latter rotation sliding along the surface of said rotated cam member to thereby return it to its original position.

4. In a transformer whose output voltage is varied by means of a tap-changer associated therewith, the combination comprising, a stop mechanism including a stop bar, a stop disk having two protruding stop members disposed to cooperate with the stop bar, two cam members for the stop disk, one of the cam members being pivoted about a point associated with one of the protruding stop members, and the other cam member being pivoted about a point associated with the other protruding stop member, means for simultaneously rotating the stop disk and for positioning the tap-changer, means for tripping the stop bar once the tap-changer has reached a predetermined position to thereby effect engag merit of the stop bar with one of the cam members, thus rotating said one of the cam members about its pivot point until it engages its associated protruding stop member, thereby preventing further rotation of the stop disk in a given direc tion and positioning of the tap-changer in a given direction, and means for preventing said one of the cam members from returning to its original position until the stop disk rotates a predeter mined distance in the opposite direction, whereby the stop bar slides along the surface of said one of the cam members as the stop disk rotates in said opposite direction to thereby effect a resetting of the stop bar.

5. In a transformer whose output voltage is varied by means of a tap-changer associated therewith, the combination comprising, a stop mechanism including a spring loaded stop bar. a stop disk having two protruding stop members disposed to cooperate with the stop bar, two L-shaped cam members for the stop disk, one of the L-shaped cam members being pivoted about a point associated with one of the two protruding stop members, the other L-shaped cam member being pivoted about a point associated with the other protruding stop member, means for simultaneously rotating the stop disk and for positioning the tap-changer, means for tripping the stop bar once the tap-changer has reached a predetermined position to thereby effect engagement of the stop bar with one of the legs of one of the L-shaped cam members, thus rotating said one of the L-shaped cam members about its pivot point until said one of the legs engages its associated protruding stop member, thereby preventing further rotation of the stop disk in a given direction and positioning of the tap-changer in a given direction, and means for preventing said one of the L-shaped cam members from returning to its original position until the stop disk rotates a predetermined distance in the opposite direction, whereby the stop bar slides along the surface of the other leg of said one of the L-shaped cam members as the stop disk rotates in said opposite direction to thereby effect a resetting of the stop bar.

6. In a transformer whose output voltage is varied by means of a tap-changer associated therewith, the combination comprising, a stop mechanism inculding a spring-loaded stop bar, a stop disk having two protruding stop members disposed to cooperate with the stop bar, means for simultaneously rotating the stop disk and positioning the tap-changer, two cam members pivoted about two predetermined points on the stop disk, each cam member having disposed therein a spring-loaded pin member, a plate member disposed to cooperate with the pin members and hold them in the spring-loaded position during the normal positioning of the tap-changer, a spring connected to each of the cam members for biasing the cam members in such a direction as to enable the plate member to hold the pin mem here in the spring-loaded position during the normal positioning of the tap-changer, means for tripping the stop bar once the tap-changer has reached a predetermined position, to thereby effect an engagement of the stop bar with one of the cam members, thus rotating said one of the cam members about its pivot point until it engages is associated protruding stop member thus preventing further rotation of the stop disk in a given direction and thereby extending the spring member and permitting the spring-loaded pin member of said one of the cam members to extend beyond the plate member to thus hold Said one of the cam members in its rotated position, and means for resttting the spring-loaded pin member of said one of the cam members once the stop disk has been rotated a predetermined distance in the opposite direction, the stop bar during a portion of this latter rotation siiding along the surface of said one of the cam members to thereby return it to its spring-loaded position.

7. In a transformer whose output voltage is varied by means of a tap-changer associated therewith, the combination comprising, a stop mechanism including a spring-loaded stop bar, a stop disk having two protruding stop members disposed to cooperate with the stop bar, means for simultaneously rotating the stop disk and positioning the tap-changer, two L-shaped cam members for the stop disk, one of the L-shaped cam members being pivoted about a point associated with one of the two protruding stop members, the other L-shape.l cam member being pivoted about a point associated with the other protruding stop member, each cam member having disposed therein a spring-loaded pin member, a plate member disposed to cooperate with the pin members and hold them in the spring-loaded position'during the normal positioning of the tapchanger, a spring connected to each-of the L- shaped cam members for biasing the L-shaped cam;members in such a directionas'to enable the platejmember to hold the pinv members in the springeloaded position during the normal positioning of the tap-changer, means for tripping the stop bar once the tap-changer has reached a predetermined position, to thereby effect an en-- gagement oi the stop bar with one of the legs of said one of the L-shaped cam members, thus rotating said one of the L-shaped cam members until'said one of the legs engages its associated protrudingstop member, thus preventing further rotation of the stop disk in a givendirectio'n and thereby extending the spring member and permitting the spring-loaded pin member of said one of the L-shaped cam members to extend bei yondithe plate member to thus hold said one of the L-shaped cam members in its. rotated position', and means for resetting the spring -loaded pin member of said one of the L-shaped cam members once the stop disk has been rotated a predetermined distance in the opposite direction,

the stop bar during a portion of this latter rotation sliding along the surface of the other leg of i said one of the L-shaped cam members to th'ereby return it to its spring-loaded pes'itionf No inferences cited. 

